Patent Literature 1 describes a technique in which a direction range in which illumination provided by a headlight of the own vehicle needs to be suppressed is calculated in accordance with a position of a lighting device of a forward vehicle detected by a sensor. Specifically, according to Patent Literature 1, a direction range which is viewed from the headlight and in which illumination provided by the headlight needs to be suppressed is calculated by performing a conversion using a distance P from a center of the own vehicle to the headlight with respect to a position of a light source of the forward vehicle detected by the sensor.